axi_sub_arb: Fix arbiter read grant condition

When 'r_pri' is not set, read operation should be granted only if
a read 'r_dv' is pending and there's no required write action 'w_dv'.

Signed-off-by: Wiktoria Kuna <wkuna@antmicro.com>

src/axi/rtl/axi_sub_arb.sv

@@ -113,7 +113,7 @@ module axi_sub_arb import axi_pkg::*; #(
 //            3'b111: r_win = 1;
 //        endcase
         if (r_pri) r_win = r_dv || !w_dv;
-        else       r_win = w_dv || !r_dv;
+        else       r_win = r_dv && !w_dv;
     end
 
     always_comb begin